Apparatus for seaming pieces of textile fabric or the like

ABSTRACT

An improvement in apparatus for joining together two pieces of material such as textile fabric. The apparatus comprises means for seaming the two pieces together and means for feeding the two pieces through the seaming means comprising a first feed device for one of said pieces and a second feed device for the other. The improvement comprises means for sensing an out-ofregistration condition of trailing ends of the two pieces fed through the seaming means; means for varying the relative speed of the two feed devices; and means responsive to the sensing means for controlling the speed-varying means to bring the trailing ends of the pieces substantially into registration.

United States Patent [1 1 Conner, Jr.

[ 1 Feb. 25, 1975 [54] APPARATUS SEAMING PIECES OF TEXTILE FABRIC OR THELIKE [75] inventor: William R. Conner, Jr., Shelbyville,

Tenn.

[73] Assignee: Stahl-Urban Company, Brookhaven,

Mass.

[22] Filed: Aug. 3, 1973 [21] Appl. N0.: 385,349

[52] U.S. Cl 112/121.l1, 112/212, 226/32, 226/115, 250/548 [51] Int. ClD05b 19/00 Field of Search. 112/212, 213, 121.11, 121.12, 112/208, 209,121.27, 132, 134,118, 86, 90, 102; 226/32, 115; 250/548 [56] ReferencesCited UNITED STATES PATENTS 3,262,410 7/1966 Chernes 112/212 3,461,8278/1969 Strobel et a1. 1l2/121.l2 X 3,559,568 2/1971 Stanley 250/548 XWillenbacher 112/212 1/1973 Hennings 250/548 X 10/1973 Matthis 226/32Primary Examiner-Richard J. Scanlan, Jr. Assistant Examiner-Peter NerbunAttorney, Agent, or Firm-Koenig, Senniger, Power and Leavitt [5 7]ABSTRACT An improvement in apparatus for joining together two pieces ofmaterial such as textile fabric. The apparatus comprises means forseaming the two pieces together and means for feeding the two piecesthrough the seaming means comprising a first feed device for one of saidpieces and a second feed device for the other. The improvement comprisesmeans for sensing an outof-registration condition of trailing ends ofthe two pieces fed through the seaming means; means for varying therelative speed of the two feed devices; and

means responsive to the sensing means for controlling the speed-varyingmeans to bring the trailing ends of the pieces substantially intoregistration.

27 Claims, 10 Drawing Figures PATENIEQ FEB2 5 I975 SHEET 1 0F 6 FIG.

APPARATUS FOR SEWING PIECES OF TEXTILE FABRIC OR THE LIKE BACKKROUND OFTHE INVENTION This invention relates to apparatus for seaming pieces oftextile fabric or the like, and more particularly to apparatus forautomatically sewing such workpieces together with their ends matching.

In many sewing operations in which two pieces of material are stitchedtogether, it is necessary to make the start and finish ends of the twopieces sew out even and match, even though the pieces may be of unequallength as received from the cutting department, and even though theremay be a tendency, in normal sewing operations in which the material isfed through the sewing machine by a feed dog from underneath, for thebottom piece of material to overfeed in relation to the top piece. Inmanual operations, the operator may effect the requisite seam endequalization by starting the sewing operation with the starting ends ofthe two pieces matched, sewing a short distance, stopping, matching thefinished ends of the two pieces and holding them between her fingerswith some tension while she guides and finishes sewing the seam. Whatthis amounts to is that the operator is compelling the two pieces tofeed at the same rate or with a shorter piece stretched slightly tomatch the longer piece. In automated sewing operations, however, therehas been a problem of providing for seam end equalization.

SUMMARY OF THE INVENTION Among the several objects of this invention maybe noted the provision of automatic seam end equalizing means forapparatus for joining together two pieces of material; the provision ofsuch means for automatic sewing apparatus, the provision of such meanswhich is accurate and reliable in operation; and the provision of suchmeans which does not complicate the introduction of the pieces ofmaterial to the sewing machine of the apparatus.

In general, apparatus ofthis invention involves means for joiningtogether two pieces of material such as textile fabric, the apparatuscomprising means for seaming the two pieces together and means forfeedingthe two pieces through the seaming means comprising a first feeddevice for one of said pieces and a second feed device for the other,with means for sensing an out-ofregistration condition of the trailingends of the two pieces fed through the seaming means, means for varyingthe relative speed of the two feed devices, and means responsive to thesensing means for controlling the speed-varying means to bring thetrailing ends of the pieces substantially into registration.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan of apparatusembodying this invention;

FIG. 2 is an enlarged vertical section taken generally on line 22 ofFIG. 1;

FIG. 3 is an enlarged vertical section taken generally on line 33 ofFIG. 1;

FIG. 4 is a view in elevation on line 4-4 of FIG. 2;

FIG. 5 is a view in elevation on line S5 of FIG. I on a larger scalethan FIG. 1;

FIG. 6 is an enlarged horizontal section taken generally on line 6-6 ofFIG. 5;

FIG. 7 is a partial side elevation taken on line 7--7 of FIGS. 1 and 5;

FIG. 8 is an enlarged fragment of FIG. 4 showing details of a resilientcoupling; and

FIGS. 9 and 10 together constitute a schematic circuit diagram of thepresent invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, firstmore particularly to FIGS. 1 and 3, there is generally indicated at lapparatus of this invention for joining together two pieces of materialA and B such as textile fabric. The apparatus generally comprises meansindicated at 3 for seaming the two pieces together, more particularly asewing machine, having means indicated generally at 5 for feeding thetwo pieces or plies" of material A and B therethrough. The feeding meanscomprises a first feed de vice 7 for one of the pieces (the bottom pieceA, as illustrated) and a second feed device 9 for the other (the toppiece B, as illustrated). The apparatus further comprises meansindicated generally at 10 for sensing an out-of-registration conditionof the two pieces A and B, e.g., an out-of-registration condition ormismatch of the trailing end of one of said pieces relative to thetrailing end of the other piece, as. they are fed through the seamingmeans (the sewing machine), and means indicated generally at 11controlled by the sensing means for varying the relative speed of thetwo feed devices 7 and 9 to correct the out--of-registration condition.

More particularly, the apparatus 1 comprises a sewing table 13 over thetop of 15 of which plies A and B are fed through the sewing machine. Thetable top 15 is of the air flotation type, having, perforations 17 inits top plate 19 through which air blows out upwardly for floating thework (i.e., plies A and B). The table has a cutout 21 in one side andthe bed 22 of sewing machine 3 extends into this cutout with the bedplate 23 of the machine flush with the top of the table. The sewingmachine is of a commercially available type, such as a Union SpecialMachine Company Style 56300AK, having the two feed devices 7 and 9incorporated therein, as to which the first (or lower) feed device 7(for the bottom pice A) is in the bed of the machine, comprising aso-called feed dog working in slots such as indicted at 25 in FIG. 3 inthe so-called throat plate 27 of the machine, and the second (or upper)feed device 9 (for the top piece B) comprises a feed dog working in thepresser foot 29 of the machine. As will be understood by those skilledin the art, the lower feed dog 7 is movable forwardly in a raisedposition through a feed stroke for feeding the lower piece A forward,then rearwardly in a lowered position through a return stroke withoutfeeding the lower piece A rearwardly, by mechanism in the bed of the:machine. The upper feed dog 9(or presser foot feedl dog as it may sometimes be called) is similarly movable forwardly in a low-' ered positionthrough a feed stroke for feeding the upper piece B forward, thenrearwardly in a raised position through a return stroke without feedingthe upper piece rearwardly, by the variable-speed drive indicated in itsentirety by the reference numeral 11 (see FIG. 4). The needle of thesewing machine is indicated at N. The apparatus may be provided with anedge contour guidance system for the plies A and B ofthe type shown inthe coassigned Conner U.S. Pat. No. 3,636,898. The variable speed drive11 has as its input the main shaft 31 of the sewing machine which, asillustrated, is driven by an electric motor 33 via a belt and pulleydrive 35 (see FIG. 4). A cam 37 constituted by a circular disk iseccentrically mounted on the shaft 31 at the back end of the sewingmachine 3 (the end away from the needle). At 39 is indicated a camfollower lever pivoted at 41 on a plate 43 at the back end of the sewingmachine 3. The lever 39 has a cam follower roller 45 at its lower endbiased into engagement with the cam 37 by a spring 47, the arrangementbeing such that the lever 39 is swung about its pivot 41 back and forththrough a stroke (the arcuate extent of which is determined by theeccentricity of the cam 37) on each revolution of the shaft 31, whichmeans that it is swung through a stroke for each stitch taken by theneedle N. A rock shaft 49 is journalled for oscillation on a horizontalaxis extending endwise of the sewing machine at one side of the sewingmachine in front and rear bearings 51 and 53. A crank 55 secured to thisshaft adjacent its back end has its lower end linked to the lever 39 byan adjustable link 57, with a pin and slot connection between the link57 and the lever 39 comprising a slot 59 in lever 39 and a pin 61 on thelink 37 movable up and down in the slot. At its end opposite the pin 61,the link has a pivot pin connection 63 with the lower end of the crank.

The means 11 controlled by the sensing means 10 comprises meansgenerally designated 65 for swinging the link 57 up and down to vary theposition of pin 61 in slot 59, thereby to vary the throw of the crank 55and hence the degree of the oscillation of the rock shaft 49. In thisregard, it will be observed that as the pin 61 is moved closer to thepivot 41, the stroke of the pin and hence the throw of the crank 55 isreduced, and as the pin 61 is moved farther from the pivot 41, thestroke of the pin and hence the throw of the crank 55 is increased.Means 65 for varying the position of the link comprises a rack 67vertically slidable in a guide 69 on the back of plate 43, with aresilient coupling 71 'between the lower end of the rack and the link57. The rack is movable up and down by a pinion 73 in mesh with therack, the pinion being mounted on the output shaft 75 of a steppingmotor 77 mounted on the front of plate 53 with shaft 75 extendingthrough a hole in the plate.

The resilient coupling 71 (see FIG. 8) comprises an upper link 79 pinnedat its upper end as indicated at 81 to the lower end of the rack and alower link 83 pinned at its lower end as indicated at 85 to the link 57.The lower link has a cage 87 secured to its upper end, this cagecomprising a lower plate 89 secured to the upper end of the link 85, andan upper plate 91 secured on the upper ends of bars 93 extending up fromthe lower plate 89. The upper link 79 extends down through a hole 95 inthe upper plate, and has a plate 97 on its lower end slidable on thebars 93. Coil compression springs 99 are interposed between plate 97 and91 and between plates 89 and 97 providing for resilient interconnectionbetween the upper and lower links, functioning to isolate the steppingmotor 77 from shock such as may be transmitted to the lower link 83 bylink 57.

An arm 101 extends down from shaft 49 adjacent the front end of thesewing machine, and has its lower end connected to the upper feed dog 9by a link 103 consti' tuted by a length of relatively thin, flexiblesteel strip. The arrangement is such that, with motor 33 in operationdriving the shaft 31 of the sewing machine 3, lever 39 is oscillated bythe cam 37, its throw being determined by the eccentricity of the cam.As the lever 39 oscillates, it oscillates crank 55 and shaft 49 via thelink 57, with the degree of oscillation of the crank 55 and shaft 49dependent upon the angle of the link 57 (or upon the position of pin 61in slot 59). The angle of the link (or the position of pin 61 in slot59) is determined bythe position of the rack 67, which is moved up ordown by the stepping motor 77 to decrease or increase the degree ofoscillation of the shaft 49. The arm 101 on shaft 49 acts to reciprocatethe upper feed dog 9, with the stroke of the feed dog 9 dependent upon.the degree of oscillation of the shaft 49, i.e., the greater the degreeof oscillation of shaft 49, the greater the stroke (for each revolutionof shaft 31) of the dog 9, and vice versa. Thus, stepping motor 77, whenenergized to rotate the pinion 73 in the direction to drive the rack 67up, acts to decrease the stroke (or speed) of the upper feed dog 9, andwhen energized to rotate the pinion 73 in the direction to drive therack down, acts to increase the stroke (or speed) of the upper feed dog.

The means 10 for sensing an out-of-registration condition of plies A andB, and more particularly a mismatch of their trailing ends, comprisestwo sensor units 105 and 107. The first sensor unit 105 has an operativeposition at a first sensing station spaced upstream from the needle N ofthe sewing machine a distance measured along the path of travel of pliesA and B corresponding generally to the length of the plies, and moreparticularly slightly greater than the length of the plies. Unit 105 isshown in its said operative position at said sensing station insolidlines in FIG. 3 and in phantom in FIG. 5. The second sensor unit 107 isfixed in position at a second sensing station spaced upstream from thesewing machine generally half said distance. The two sensing units aregenerally identical, each comprising a three-timed fork designated inits entirety by the reference numeral 109, and made up of a center bar111 flanked by outside bars 113 and 115 which have outer ends 117 and119 flaring away from the outer end portion of the center bars. Thelatter is reduced in thickness as indicated at 121 to provide slots 123and 125 for receiving themargins of plies A and B and tapered asindicated at 127. Sensor unit 105 has means for sensing the passage ofthe trailing end of ply A through slot 123 and means for sensing thepassage of the trailing end of ply B through slot 125. The first ofthese means comprises a light emitting diode LEDl mounted in an openingin bar 113 and a phototransistor Q1 mounted in a recess in center bar111 opposite diode LEDl. The second means similarly comprises a. lightemitting diode LEDZ mounted in an opening in bar 115 and aphototransistor Q2 mounted in a recess in center bar 111 opposite diodeLED2. Sensor unit 107 similarly has means comprising a light emittingdiode LED3 and a phototransistor Q3 for sensing the passage of thetrailing end of ply A through its slot 123 and means comprising a lightemitting diode LED4 and a phototransistor Q4 for sensing the passage ofthe trailing end of ply B through its slot 125.

At the rear end of the top of table 13 (rear meaning upstream inrelation to the direction of travel of the plies A and B toward thesewing machine) is a guide 129 for guiding plies A and B travelingupwardly at the rear of the table around onto the top of the table. Thisguide comprises a length of tubing pinned at one end as indicated at 131to an adjustable bracket 133 extending rearwardly at the left rearcorner of the table top (left as viewed in the direction of travel ofthe plies toward the sewing machine) and secured at its} other end asindicated at 135 to an angle iron 137 (seeLFlGS. 1, 3, 5 and 7)extending rearwardly from the table top at its right rear corner. Guide129 may be angled as shown in FIG. 1 relative to the rear edge of thetable top. A bracket 139 secured to the angle iron carries the sensorunit 107 in fixed position at the aforesaid second sensing stationlocated slightly to the rear of and below the guide 129 at the rightrear corner of the table top with the unit 107 extending generallyhorizontally from the bracket generally parallel to the rearward edge ofthe table top, and with its slotted end toward the left (as viewed inFIG. 5).

The sensor unit 105 is mounted for vertical movement between itsoperative position at. the stated first sensing station (in which it isshown in solid lines in FIG. 3 and in phantom in FIG. 5) and a raisedposition directly below and adjacent unit 107 by means generallydesignated 141 in FIGS. 5-7 for facilitating entry of plies A and B inthe two sensor units as will appear. Means 141 comprises two rods 143and 145 extending vertically between a lower bracket 147 extendingrearwardly from the right rear table leg 149 and the bracket 139. Thesensor unit 105 is carried. by a tubular slide 151 slidable up and downon rod 143 extending generally horizontally parallel to sensor 107 belowand in line with the latter. Unit 105 is maintained in line with unit107 via a tee 153 on slide 151 carrying a pair of rollers 155 which rideon opposite sides of bar 145. An air cylinder 157 is provided for movingthe sensor unit 105 up and down between its lowered sensing position andits raised ply-inserting position. This cylinder extends verticallybetween brackets 147 and 139 and has its piston rod 159 extendingdownwardly from its piston (not shown) through a hole in bracket 147with a yoke 161 at the lower end of the piston rod and rod 163 extendingup from the yoke through a hole in bracket 147 to a connection at 165with the tee 153. The arrangement is such that on extending the pistonrod 159 the unit 105 is moved down to its operative position, and onretracting the piston rod the unit 105 is raised to its ply-insertingposition.

Unit 105, when raised, is directly below and adjacent unit 107 forsimultaneous insertion of ply A in slots 123 and ply B in slots 125 ofthe two units. After insertion of the plies, unit 105 is lowered to itsoperative position of FIG. 3, wherein it functions to sense any mismatchof the trailing ends of plies A and B at the start ofa sewing operationas they pass upwardly through unit 105. Thus, if the trailing end of plyA leads the trailing end of ply B, phototransistor O1 is activatedbefore phototransistor 02, and vice versa. Sensor 107 functions to senseany mismatch of the trailing ends of plies A and B halfway through asewing operation as the plies pass through unit 107. Thus, if thetrailing end of ply A leads the trailing end of ply B at unit 107 (i.e.,at the second sensing station), phototransistor Q3 is activated beforephototransistor Q4, and vice versa.

A schematic diagram of the circuitry employed in the present inventionis shown in FIGS. 9 and 10. Most of the circuitry in FIGS. 9 and 10 maybe conveniently divided into a rack centering section 201, a firstmeasurement and adjustment section 203, a second measurement andadjustment section 205, a motor control section 207, and the dc.stepping motor 77. The motor control section and the stepping motorcomprise means for actuating variable-speed drive 11.

A motor control section has three inputs 211, 213 and 215. A high signalat input 211 will cause the motor control section to set the motor torotate in a forward" direction and a high signal at input 213 will causethe motor control section to set the motor to rotate in a reversedirection. Motor 77 does not begin to step until a proper time-varyingvoltage is supplied to input 215, at which time the motor will move onestep in the predetermined direction for each cycle of the time-varyingvoltage.

To permit ease in understanding the remaining circuitry, the operationof motor control section 207 and dc. stepping motor 77 will be explainedat this point.

Stepping motor 77 is of the commercially available type having aplurality of windings (such as two windings), the rotor shaft of themotor being adapted to rotate with stepwise movements when the windingsare energized with successive sequential changes in polarity, i.e., andas will be understood by those skilled in the art, a stepwise movementof the motors shaft occurs when the polarity of a first one of thewindings is reversed while maintaining the same polarization of thesecond winding. Then another stepwise movement in the same directionoccurs by reversing the polarity of the second winding while maintainingthe same polarization of the first winding, and so on. To change thedirection of shaft rotation, the windings are energized with a reversedsequence of successive alternate changes in polarity, i.e., one of thetwo windings has its polarity reversed twice in succession without anintervening reversal of the polarity of the other winding.

Preferably, stepping motor 77 is of a socalled bifilar type having twowindings each of two halves. That is, each winding has two sections orcoils wound in opposite directions. Stepping motor 77 has a firstwinding with two coils or sections 265a, 26511 and a second winding withsections 267a, 2671;. Each half or section ofa winding is adapted, whenenergized, to polarize the respective winding in one direction. Thehalves of each winding are alternately energized for alternatelypolarizing the winding.

Referring to motor control section 201, input 215 is connected to thetoggle (or clock) input of a flip-flop FF4. The conventional powersupply connections for this flip-flop, and for certain other portions ofthe cir cuitry, are not shown in order to simplify the drawings.

As is known to those in the electronics art, a flip-flop constitutes abistable device having a pair of stable states. Such a device is adaptedto be switched alternately from one state to the other. Flip-flop FF4 isknown as a toggle-type flip-flop, i.e., when toggled, the flip-f1opswitches from a state in which one of its outputs Q or Q is high and theother low to a state in which the former is low and the latter is high.Another type of flip-flop (discussed below) is known as an S-Rflip-flop. This type of flip-flop has S and R inputs and Q and Qoutputs. When a signal is present at the R in put, the Q output is highand the Q output low. When a signal is applied to the S input, theflipflop changes its state so that the Q output is low and the Q outputis high.

Further circuitry of motor control section 207 may logically be dividedinto a portion for causing motor 77 to step and a portion for settingthe motor to rotate in either a forward or a reverse direction.

The portion of the circuitry for effecting stepping of the motor 77includes the flip-flop F1 4 which is toggled by each cycle of thetime-varying voltage supplied through input 215. Interconnected with theoutputs of flip-flop FF4 is a plurality of AND gates G79, G81, G83 andG85, each of which has a pair of inputs and a single output. The Qoutput of flip-flop FF4 is commonly connected to an input of G79 and aninput of G81, while the Q output of FF4 is commonly connected torespective inputs of gates G83 and G85. The remaining inputs of G79,G81, G83 and G85, i.e., those not connected to the outputs of FF4, willbe referred to as enable" inputs and are indicated by e.

Interconnected with gates G79, G81, G83 and G85 are a pair of S-R typeflip-flops FPS and FF6 (note the discussion above of the R-S type offlip-flop). The respective outputs of AND gates G79 and G81 areconnected to the R and S inputs of FFS, while the respective outputs ofAND gates G83 and G85 are connected to the S and R inputs of FF6. Therespective Q and Q outputs of flip-flops FPS and FF6 are connected tothe enable inputs of AND gates G83, G85, G79 and G81, respectively.Therefore. gates G79, G81, G83 and G85 are adapted to sense and beresponsive to the state of energization of the respective outputterminals of flipflops FPS and FF6.

The respective Q and Q outputs of flipflops FPS and FF6 are alsoconnected to a plurality of switching-type amplifiers (A5, A6, A3 andA4, respectively) to control switching of energization of respectivewinding sections (267b, 267a, 265a, 265b) of stepping motor 77.

When winding sections 265a and 267b are energized, then only AND gatesG79 and G83 have their enable inputs e energized. Upon flip-flop FF4being toggled to change state, its Q output goes high and its Q ouptutgoes low. AND gate G79 will then provide a high output to the R input offlip-flop FFS, causing it to switch states thereby energizing windingsection 267a and enabling AND gate G85 while deenergizing windingsection 267b and disabling AND gate G83. When flip-flop FF4 is nexttoggled, its Q output will be switched low and its Q output high. Theoutput of AND gate G85 will provide a high output to the R input offlip-flop FF6, causing it to switch state thereby energizing windingsection 265b and enabling AND gate G81 while deenergizing windingsection 265a and AND gate G79.

The portion of the circuit for setting the motor to rotate shaft 75 ineither a forward or a reverse direction includes a further S-R typeflip-flop FF7 which has its S input connected to input 211, its R inputconnected to input 213, and its Q output connected to switching circuitMZ. Switching circuit MZ interconnects the outputs of flip-flops FF5with motor winding sections 267a and 267b and is connected to the Qoutput of flipflop FF7.

Switching circuit M2 is preferably a multiplexer of the integratedcircuit type and effects internal switching each time flip-flop FF7changes state so that the connection of a respective input to arespective output is reversed. This section of the circuit, therefore,effects reversal of the polarity of one of the windings twice insuccession without an intervening reversal of the polarity of the otherwinding thereby changing the direction of rotation of motor 77 inresponse to FF7 changing state.

The output shaft of motor 77 rotates pinion 73 which drives rack 67.Rack 67 controls the stroke of the top feed dog 9 so that when shaft 75is rotated in the forward" direction the rack is driven down to increasethe stroke of the top feed dog so the top ply B is driven at a fasterrate. On the other hand, if shaft 75 is rotated in the reversedirection, the rack is driven up and decreases the stroke of the topfeed dog so that the top ply is driven at a slower rate.

The circuitry functions first to bring the rack controlling the strokeof the top feed dog to a starting or null position so that both feeddogs will start feeding the plies at the same rate. It next functions tomeasure the difference in length of the two plies as they pass the firstsensor unit and to adjust the position of the rack to change the strokeof the top feed dog to compensate for the difference in length of theplies by the time the plies progress from the first sensor unit to thesewing machine 3. Finally the circuitry functions to measure thedifference in length of the two plies as they pass the second sensorunit 107 located halfway between the first sensor unit and the sewingmachine, to compare the distance measured at the second sensor unit withone-half the distance measured at the first sensor unit, and to readjustthe position of the rack if required. The adjustment made in response tothe measurement at the first sensor unit may be considered a relativelycoarse adjustment while the adjustment associated with the second sensorunit may be considered a vernier adjustment.

In the operation of the apparatus, the operator positions plies A and Bon the top 15 of the sewing table 3 with the leading ends of the pliesgenerally matched (i.e., in registration) and located at the sewingmachine and with the plies hanging down at the rear of the table aroundthe guide 129. With the first sensor unit 105 in its raised position asindicated in phantom in FIG. 5, the operator inserts ply A in slot 123of the second sensor unit 107 and in slot 123 of the raised first sensorunit 105, and inserts ply B in slot 125 of unit 107 and in slot 125 ofunit 105. The positioning of sensor unit 105 in raised position directlyunderneath unit 107 facilitates the entry of the margins of the plies inthe slots of the sensor units. The unit 105 is then lowered to itsoperative position (shown in solid lines in FIGS. 3 and 5) in which thetrailing ends of the plies are somewhat upstream from (downwardly of)the sensor unit 105. This allows the centering section 201 to return therack 67 to its starting position before a measurement of the differencein length of the two plies is made at the first sensor station.

Operation of the seam end equalizer then proceeds by actuation of aswitch SW1 which energizes or applies a signal to the S input of aflip-flop FFl. The Q output of flip-flop FF] is connected to input 213of the motor control section through an AND gate G1, an EXCLUSIVE ORgate G3, a switching circuit M1, and an amplifier A1.

Switching circuit M1 is a monolithic digital multiplexer comprising fourmultiplexing circuits with common select (pin P1) and enable (pin P15)logic. The multiplexer is the logical implementation of a fourpole,two-position switch, with the position of the switch being set by thelogic level supplied to the select input (P1). The respective inputs forthe three multiplexing circuits used are P2 and P3, P and P11, and P13and P14 while the respective outputs are P4, P9 and P12. With a lowlogic level signal at pin P1, pins P2 and P4, P11 and P9, and P14 andP12 are respectively interconnected. However, if a high signal issupplied at pin P1, the multiplexing circuits switch interconnectingpins P3 and P4, P10 and P9, and P13 and P12, respectively. A high signalat the enable pin P15 disables all outputs. The multiplexing circuitincluding pins P2, P3 and P4 is employed in providing a time-varyingvoltage required in driving motor 77 while two other multiplexingcircuits, including pins P12, P13, P14 and P9, P10, P11, respectively,are used in setting motor control section 207 to drive the rack eitherup or down.

Upon actuation, switch SW1 provides a signal to the S input of flip-flopFFl, causing the Q output of FFl to go high. This high signal issupplied to input 213 of the motor control section, causing motor 77 tobe set to drive the rack up.

The high signal at the Q output of PH also enables an AND gate G5 topass oscillations from a lowfrequency oscillator 221 to input 215 of themotor control section through an EXCLUSIVE OR gate G7, multiplexer M 1,and an AND gate G9. For each oscillation from oscillator 221, motor 77will rotate one step in the reverse direction, driving rack 67 up.

Motor 77 will continue to drive the rack 67 up in a stepwise manneruntil either a sensor 223 detects passage of an aperture 225 in rack 67or a cam surface 227 on the rack 67 strikes an actuating arm 229 of aswitch SW2. Sensor 223 comprises a light emitting diode LED 5, aphototransistor Q5 and a resistor R5. The collector of transistor Q5 isconnected to a positive voltage supply +V through resistor R1 while itsemitter is grounded. The rack being detected blocks the'light of LED 5from impinging on transistor Q5, rendering Q5 nonconductive. When sensor223 detects aperture 225, transistor 05 becomes conductive, causingsensor 223 to provide a low output signal.

Assuming that the original position of the aperture 225 is above LED 5,the rack will continue moving up until cam surface 227 strikes actuatingarm 229, indicating that the maximum upward travel of the rack has beenreached. Upon actuation, SW2 provides a signal to the S input of aflip-flop FF2 through an AND gate.

G11 and a NOT gate G13, causing FF2 to change state so that its Q outputprovides a low signal which disables gate G1 and thereby causes the highsignal from the Q output of PH to be removed from the input 213 of themotor control section. The O output of flip-flop FF2 supplies a highsignal to input 211 of the motor control multiplexer M1, and anamplifier A2 thereby causing motor 77 to reverse its direction ofrotation. The Q output of flip-flop FF2 also enables an AND gate G19.

The rack will be driven down until aperture 225 falls into registrationwith sensor 223. When the rack is centered, sensor 223, connected to theR inputs of flipflops FFl and FFZ through a NAND gate G17, AND gate G19,and a NOT gate G21, provides a signal causing both flip-flops to changestate thereby stopping section 207 through an EXCLUSIVE OR gate G15,

motor 77 and returning the centering section circuitry to a quiescentstate.

As previously indicated, first sensor unit includes a sensor comprisinglight emitting diode LED 1 and phototransistor Q1 for detecting passageof the trailing edge of the bottom ply A and a sensor comprising LED 2and Q2 for detecting passage of the trailing edge of the top ply B. Theemitters ofQl and O2 are grounded while their collectors are connectedto +V through a resistor R1 and a resistor R2, respectively.

Assuming the top ply B to be the shorter, when it passes phototransistorQ2, the collector of which is connected to an AND gate G23 through aNAND gate G25, an AND gate G27, a NOT gate G29, and an EX- CLUSIVE ORgate G31, Q2 provides an output signal enabling gate G23. Oscillationsfrom a high-frequency oscillator 235 pass through enabled gate G23 to acounter 237 and a toggle-type flip-flop FF3. For simplicity, the countaccumulated by counter 237 will be referred to as the A count. Thefunction of flip-flop FF3 will be discussed below.

A comparator 239 is used to compare the A count with a B countaccumulated by a counter 241. The output of comparator 239 provides ahigh output when the A count is greater than the E count. The output ofcomparator 239 is commonly connected to enable an AND gate G33 and toinput P1 of multiplexer M1 to cause switching of the multiplexercircuits so that the respective outputs are connected to P3, P10 andP13, respectively. The output of phototransistor 02, connected to input213 of the motor control section 207 through gates G25 and G27,multiplexer M1 and amplifier A1, sets motor 77 to drive the rack up.

When the bottom ply passes unit 105, gate G23, connected to thecollector of Q1 through a NAND gate G34, an AND gate G35, a NOT gateG37, and gate G31, becomes disabled, stopping the counting of counter237. The count stored in counter 237 represents both a measurement ofthe time period between passage of the trailing ends of the two plies bysensor unit 105 and the correction (in steps of motor 77) needed to slowthe feed rate of the top feed dog 9 so that the trailing ends of the twoplies will come out in registration at the needle.

Since both plies have passed first sensor unit 105, an AND gate G39,which has its input terminals connected to the outputs of bothph-ototransistors (Q1 and Q2), provides an output enabling an AND gateG41 and an AND gate G43. This allows lowfrequency oscillator 221 tosupply a time-varying voltage to input 215 of the motor control section207, causing motor 77 to drive rack 67 upwardly, shortening the strokeof the top feed dog. Counter 241, connected to oscillator 221 throughgates G41 and G43, accumulates a count of the number of steps the motorhas driven.

When comparator 239 determines that the feed rate v of the top ply hasbeen sufficiently slowed (i.e., the A count equals the B count), theoutput of comparator 239 supplies a low signal which disables gate G43thereby stopping motor 77. The low output of comparator 239 also causesmultiplexer M1 to switch so that its respective outputs areinterconnected to inputs P2, P11 and P14, respectively.

Each high-frequency oscillation registered by counter 237 causedtoggling of flip-flop FF3. A counter 243 connected to the Q output ofFF3 through an EX- CLUSIVE OR gate G45 therefore accumulated a countequal to one-half the A count. The count accumulated in counter 243 willbe referred to as the C count".

The second sensor unit 107 includes a sensor comprising light emittingdiode LED 3 and phototransistor Q3 for detecting passage of the trailingedge of the bottom ply A and a sensor comprising LED 4 and Q4 fordetecting passage of the trailing edge of the top ply B. The emitters ofQ3 and Q4 are grounded while their collectors are connected to positivevoltage through a resistor R3 and a resistor R4, respectively.

As the top ply B progresses toward the sewing machine, it passes thesecond sensor unit 107. The output of Q4 enables an AND gate G47 whichis connected to the collector of Q4 through a NAND gate G49, an AND gateG51, a NOT gate G53, and an EXCLUSIVE OR gate G55. The output of Q4 alsocauses a high signal to be supplied to the enable input P of multiplexerMl thereby disabling all outputs of the multiplexer.

Oscillations from high-frequency oscillator 235 are supplied to afurther counter 249 through enabled AND gate G47 and an EXCLUSIVE ORgate G57. The count accumulated by counter 249 will be referred to asthe D count.

When the bottom ply passes the second sensor unit, gate G47, which isconnected to the collector of Q3 through a NAND gate G59, an AND gateG61, a NOT gate G63 and gate G55, becomes disabled, stopping counter249. The count stored in counter 249 is then analogous to the timeperiod between the passage of the trailing ends of the two plies bysecond sensor unit 107. The high signal at the enable input P15 ofmultiplexer M1 is removed, enabling the various outputs of M1. Sinceboth plies have passed the second sensor unit, an AND gate G65, havingits inputs connected to the outputs of both Q3 and Q4, provides a highoutput enabling an AND gate G67 and an AND gate G69. Also, an AND gateG70 (connected to both Q3 and Q4) provides an output to the S input offlip-flop FF3, causing the output of FF3 to provide a low signal.

A comparator 251 compares the C count and the D count. If C equals D, nofurther adjustment in the stroke of the top feed dog 9 is requiredbecause onehalf the difference in length of the two plies has beencorrected in one-half the distance to the sewing machine. If C is lessthan D, an undercorrected condition exists so that the stroke of the topfeed dog must be shortened to further slow the feed rate of the top plyB. Finally, if C is greater than D, an overcorrected condition exists sothat the stroke of the top feed dog must be lengthened to feed the topply at a faster rate al- I though still slower than the feed rate of thebottom ply.

Comparator 251 has an output 253 which will provide a high output if Cis greater than D and an output 255 which will provide a high output ifC is less than D.

If C is greater than D, a high signal will be supplied from output 253to motor control section input 211 through gate G15, multiplexer M1, andamplifier A2 thereby setting motor 77 to drive rack 67 down. The highsignal at output 253 also enables an AND gate G71 connected to output253 through gate G69. This allows oscillations from low-frequencyoscillator 221 to be supplied to input 215 of the motor control sectionthrough enabled AND gate G67, enabled AND gate G71, an EXCLUSIVE OR gateG73, EXCLUSIVE OR gate G7, multiplexer M1 and AND gate G9, causing themotor to drive rack 67 down thereby increasing the 12 feed rate of thetop ply. Counter 249, being connected to gate G71 through an AND gateG75 and EXCLU- SIVE OR gate G57, increases the D count with every stepof the motor until C equals D, at which time output 253 provides a lowsignal, disabling gate G71 and stopping the motor.

On the other hand, if the C count had been less than the D count, a highsignal would have been supplied from output 255 of comparator 251 toinput 213 of motor control section 207 through EXCLUSIVE OR gate G3,multiplexer M1, and amplifier A1 so as to set the motor to drive rack 67up. The high signal at output 255 also would have enabled an AND gateG77, allowing oscillations from lowfrequency oscillator 221 to have beensupplied to motor control section input 215 through gate G67, gate G77,gate G45, gate G73, gate G7, multiplexer M1, and gate G9, causing themotor to drive rack 67 up thereby further slowing the feed rate of thetop ply. Counter 243, being connected to gate G45, would increase the Ccount with every step of motor 77 until C equals D, at which time output253 would have provided a low output, disabling gate G77 and stoppingthe motor.

The operation of the apparatus has been described above for a conditionwherein the top ply B is shorter than the bottom ply A. The operationfor the condition wherein the top ply B is longer than the bottom ply Ais similar to the above and is not believed to require detaileddescription.

It will be understood that the apparatus may include an edge contourguidance control for plies A and B of the type illustrated in US. Pat.No. 3,636,898, issued Jan. 25, 1972.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. In apparatus for joining two pieces of material such as textilefabric, said apparatus comprising means for seaming the two piecestogether and means for feeding the two pieces through the seaming meanscomprising a first feed device for one of said pieces and a second feeddevice for the other, the improvement comprising the provision of:

means for sensing an out-of-registration condition of the trailing endof one of said pieces relative to the trailing end of the other piece assaid pieces are fed through the seaming means;

means for varying the relative speed of the two feed devices; and

means responsive to the sensing means for controlling the speed-varyingmeans to bring the trailing ends of the pieces substantially intoregistration one with the other.

2. In apparatus as set forth in claim 1, the speedvarying meanscomprising a variable speed drive for one of said feed devices, and thecontrol means comprising means for controlling said variable speed driveto vary the speed of said one feed device.

3. In apparatus as set forth in claim 2, the sensing means comprising aplurality of sensor units each for sensing out-of-registrationconditions of the trailing end of one of said pieces relative to thetrailing end of the other piece at a corresponding plurality of stationsin the path of travel of the pieces.

4. In apparatus as set forth in claim 3, said sensing means comprisingtwo sensor units, a first of which has an operative position spacedupstream from said seaming means a distance measured along the path oftravel of said pieces corresponding generally to the length of saidpieces, and the second of which is spaced generally half said distanceupstream from said seaming means.

5. In apparatus as set forth in claim 4, each of said sensor unitscomprising a first sensor for sensing passage of the trailing end of onepiece and a second sensor for sensing passage of the trailing end of theother piece.

6. In apparatus as set forth in claim 1, the sensing means comprising asensor unit including a first sensor for sensing the passage of thetrailing end of one piece and a second sensor for sensing the passage ofthe trailing end of the other, each sensor comprising a pair of elementsadapted to be positioned along the pathof travel of a respective pieceand adjacent thereto, said elements adapted to actuate an electricalcircuit to provide a signal upon the passage thereby of the trailing endof said respective piece.

7. In apparatus as set forth in claim 6, one of said sensor elementscomprising a light source and the other comprising a light sensitivedevice.

8. In apparatus as set forth in claim 7, said light source comprising alight emitting diode, and said light sensitive device comprising aphototransistor.

9. In apparatus as set forth in claim 2, said control means furthercomprising means for measuring the magnitude of the out-of-registrationcondition of the trailing end of one of said pieces relative to thetrailing end of the other piece, said means for controlling the variablespeed drive being responsive to said measurement means.

10. In apparatus as set forth in claim 9, the measurement meanscomprising counter means for registering the magnitude of theout-of-registration condition as the pieces pass said sensing means andmeans for correcting the speed of the variable speed drive to effect achange in speed of said one feed device so as to bring the trailing endssubstantially into registration one with the other when they reach saidseaming means.

11. In apparatus as set forth in claim 9, the measurement meanscomprising counter means for registering the magnitude of theout-of-registration condition as the pieces pass said sensing means andfor registering the magnitude of correction made by said variable speeddrive and comparison means for determining when said variable speeddrive has changed the speed of said one feed device so as to bring thetrailing ends substantially into registration when they reach saidseaming means.

12. In apparatus as set forth in claim 1, the speedvarying meanscomprising a variable speed drive for one of said feed devices, thecontrol means including a stepping motor for controlling the variablespeed drive and further comprising a counter adapted to accumulate acount analogous to the time period between the passage of the twotrailing ends of the pieces by the sensing means and equal to the numberof steps of said motor required to vary the speed of one feed device tobring the trailing ends of the pieces substantially into registration ina preselected length of travel of the trailing ends of said pieces.

13. In apparatus as set forth in claim 12, said control means furthercomprising means adapted to initiate stepping of said motor after thetrailing end of the longer piece passes said sensing means.

14. In apparatus as set forth in claim 13, said control means furthercomprising a second counter adapted to accumulate a count equal to thenumber of steps taken by said motor and a comparator adapted to stopsaid stepping motor from further adjusting said variable speed drivewhen the count accumulated by said second counter equals the countaccumulated by the fir,t counter.

15. In apparatus as set forth in claim 4, said control means furthercomprising first means responsive to said first sensor unit formeasuring the magnitude of the out-of-registration condition of thetrailing ends of the two pieces at a distance measured along the path oftravel of said pieces corresponding generally to the length of saidpieces and a second means responsive to said second sensor unit formeasuring the magnitude of the out-of-registration condition of thetrailing ends of the two pieces at a distance measured along the path oftravel of said pieces corresponding generally to half the length of saidpieces, said means for controlling the variable speed drive beingsequentially responsive to both of the measurement means.

16. In apparatus as set forth in claim 15, each of the measurement meanscomprising counter means for registering the magnitude of respectiveout-of'registration conditions as the pieces pass the respective sensorunits and means responsive to said counter means for correcting thespeed of the variable speed drive to effect a change in speed of saidone feed device so as to bring the trailing ends substantially intoregistration when they reach said seaming means.

17. In apparatus as set forth in claim 15, each of the measurement meanscomprising counter means for registering the magnitude of respectiveout-of-registration conditions as the pieces pass the respective sensorunits and for registering the magnitude of correction made by saidvariable speed drive and comparison means for determining when saidvariable speed drive has changed the speed of said one feed device tobring the trailing ends of the pieces substantially into registration atsaid seaming means.

18. In apparatus as set forth in claim 4, said means for actuating thevariable speed drive comprising a stepping motor, said control meansfurther comprising a counter adapted to accumulate a count analogous tothe time period between the passage of the two trailing ends of thepieces by the first sensor unit and equal to the number of steps of saidmotor required to vary the speed of the one feed device to bring thetrailing end of the pieces substantially into registration in a lengthof travel of the trailing ends of said pieces generally corresponding tothe length of said pieces.

19. In apparatus as set forth in claim 18, said control means furthercomprising means adapted to initiate stepping of said motor after thetrailing end of the longer piece passes said first sensor unit.

20. In apparatus as set forth in claim 19, said control means furthercomprising a second counter adapted to accumulate a count equal to thenumber of steps made by said motor and a comparator adapted to stop saidstepping motor from further adjusting said variable speed drive untilsaid trailing ends have both passed said second sensor unit when thecount accumulated by said first counter equals the count accumulated bythe second counter.

21. In apparatus as set forth in claim 20, said control means furthercomprising a third counter adapted to accumulate a count equal toone-half the count accumulated by the first counter; a fourth counteradapted to accumulate a count analogous to the time period between thepassage of the two trailing ends by said second sensor unit; and asecond comparator adapted to cause said stepping motor to drive a numberof steps equal to the difference in the count accumulated by said thirdcounter and the count accumulated by said fourth counter, said secondcomparator causing said stepping motor to vary the speed of said onefeed device to bring the trailing ends of the pieces substantially intoregistration in a length of travel of the trailing ends of said piecesgenerally corresponding to half the length of said pieces.

22. In apparatus as set forth in claim 1, means for causing both feeddevices to feed at substantially the same rate before said sensing meanshas sensed an outof-registration condition of the trailing end of one ofsaid pieces relative to the trailing end of the other.

23. In apparatus as set forth in claim 2, said control means furthercomprising means for causing the one feed device to feed atsubstantially the same rate as the other feed device before the sensingmeans has sensed an out-of-registration condition of the trailing endsof the two pieces, said means for controlling the variable speed drivebeing responsive to the means for causing both feed devices to feed atsubstantially the same rate.

24. In apparatus as set forth in claim 23, said means for causing bothfeed devices to feed at substantially the same rate comprising a sensoradapted to provide a signal when both feed devices are feeding atsubstantially the same rate, the control means being responsive to saidsignal to cease further adjustment of the variable speed drive until thetrailing ends of the two pieces have passed the sensing means.

25. In apparatus as set forth in claim 1, the speedvarying meanscomprising means for varying the speed of one feed device, the otherfeed device operating at a substantially constant rate.

26. In apparatus as set forth in claim 4, means mounting said firstsensor unit for movement between its operative position and a positionadjacent said second sensor unit for facilitating entry of the piecesinto the two sensor units.

27. Apparatus for joining two pieces of material such as textile fabriccomprising:

means for seaming the two pieces of material together;

means for feeding the two pieces through the seaming means comprising afirst feed means for one of said pieces and a second feed means for theother with one of the latter a variable speed feed means; means forsensing any out-of-registration condition of the trailing end of one ofsaid pieces relative to the trailing end of the other piece as they arefed through the seaming means by the feed means; and means controlled bysaid sensing means for varying the speed of the variable speed feedmeans to vary the speed of feed of the piece of material being fedthereby through the seaming means to bring the trailing ends of thepieces substantially into registration one with the other.

1. In apparatus for joining two pieces of material such as textilefabric, said apparatus comprising means for seaming the two piecestogether and means for feeding the two pieces through the seaming meanscomprising a first feed device for one of said pieces and a second feeddevice for the other, the improvement comprising the provision of: meansfor sensing an out-of-registration condition of the trailing end of oneof said pieces relative to the trailing end of the other piece as saidpieces are fed through the seaming means; means for varying the relativespeed of the two feed devices; and means responsive to the sensing meansfor controlling the speedvarying means to bring the trailing ends of thepieces substantially into registration one with the other.
 2. Inapparatus as set forth in claim 1, the speed-varying means comprising avariable speed drive for one of said feed devices, and the control meanscomprising means for controlling said variable speed drive to vary thespeed of said one feed device.
 3. In apparatus as set forth in claim 2,the sensing means comprising a plurality of sensor units each forsensing out-of-registration conditions of the trailing end of one ofsaid pieces relative to the trailing end of the other piece at acorresponding plurality of stations in the path of travel of the pieces.4. In apparatus as set forth in claim 3, said sensing means comprisingtwo sensor units, a first of which has an opErative position spacedupstream from said seaming means a distance measured along the path oftravel of said pieces corresponding generally to the length of saidpieces, and the second of which is spaced generally half said distanceupstream from said seaming means.
 5. In apparatus as set forth in claim4, each of said sensor units comprising a first sensor for sensingpassage of the trailing end of one piece and a second sensor for sensingpassage of the trailing end of the other piece.
 6. In apparatus as setforth in claim 1, the sensing means comprising a sensor unit including afirst sensor for sensing the passage of the trailing end of one pieceand a second sensor for sensing the passage of the trailing end of theother, each sensor comprising a pair of elements adapted to bepositioned along the path of travel of a respective piece and adjacentthereto, said elements adapted to actuate an electrical circuit toprovide a signal upon the passage thereby of the trailing end of saidrespective piece.
 7. In apparatus as set forth in claim 6, one of saidsensor elements comprising a light source and the other comprising alight sensitive device.
 8. In apparatus as set forth in claim 7, saidlight source comprising a light emitting diode, and said light sensitivedevice comprising a phototransistor.
 9. In apparatus as set forth inclaim 2, said control means further comprising means for measuring themagnitude of the out-of-registration condition of the trailing end ofone of said pieces relative to the trailing end of the other piece, saidmeans for controlling the variable speed drive being responsive to saidmeasurement means.
 10. In apparatus as set forth in claim 9, themeasurement means comprising counter means for registering the magnitudeof the out-of-registration condition as the pieces pass said sensingmeans and means for correcting the speed of the variable speed drive toeffect a change in speed of said one feed device so as to bring thetrailing ends substantially into registration one with the other whenthey reach said seaming means.
 11. In apparatus as set forth in claim 9,the measurement means comprising counter means for registering themagnitude of the out-of-registration condition as the pieces pass saidsensing means and for registering the magnitude of correction made bysaid variable speed drive and comparison means for determining when saidvariable speed drive has changed the speed of said one feed device so asto bring the trailing ends substantially into registration when theyreach said seaming means.
 12. In apparatus as set forth in claim 1, thespeed-varying means comprising a variable speed drive for one of saidfeed devices, the control means including a stepping motor forcontrolling the variable speed drive and further comprising a counteradapted to accumulate a count analogous to the time period between thepassage of the two trailing ends of the pieces by the sensing means andequal to the number of steps of said motor required to vary the speed ofone feed device to bring the trailing ends of the pieces substantiallyinto registration in a preselected length of travel of the trailing endsof said pieces.
 13. In apparatus as set forth in claim 12, said controlmeans further comprising means adapted to initiate stepping of saidmotor after the trailing end of the longer piece passes said sensingmeans.
 14. In apparatus as set forth in claim 13, said control meansfurther comprising a second counter adapted to accumulate a count equalto the number of steps taken by said motor and a comparator adapted tostop said stepping motor from further adjusting said variable speeddrive when the count accumulated by said second counter equals the countaccumulated by the first counter.
 15. In apparatus as set forth in claim4, said control means further comprising first means responsive to saidfirst sensor unit for measuring the magnitude of the out-of-registrationcondition of the trailing ends of the two pieces at a distance measuredalong the path of travel of said pieces corresponding generally to thelength of said pieces and a second means responsive to said secondsensor unit for measuring the magnitude of the out-of-registrationcondition of the trailing ends of the two pieces at a distance measuredalong the path of travel of said pieces corresponding generally to halfthe length of said pieces, said means for controlling the variable speeddrive being sequentially responsive to both of the measurement means.16. In apparatus as set forth in claim 15, each of the measurement meanscomprising counter means for registering the magnitude of respectiveout-of-registration conditions as the pieces pass the respective sensorunits and means responsive to said counter means for correcting thespeed of the variable speed drive to effect a change in speed of saidone feed device so as to bring the trailing ends substantially intoregistration when they reach said seaming means.
 17. In apparatus as setforth in claim 15, each of the measurement means comprising countermeans for registering the magnitude of respective out-of-registrationconditions as the pieces pass the respective sensor units and forregistering the magnitude of correction made by said variable speeddrive and comparison means for determining when said variable speeddrive has changed the speed of said one feed device to bring thetrailing ends of the pieces substantially into registration at saidseaming means.
 18. In apparatus as set forth in claim 4, said means foractuating the variable speed drive comprising a stepping motor, saidcontrol means further comprising a counter adapted to accumulate a countanalogous to the time period between the passage of the two trailingends of the pieces by the first sensor unit and equal to the number ofsteps of said motor required to vary the speed of the one feed device tobring the trailing end of the pieces substantially into registration ina length of travel of the trailing ends of said pieces generallycorresponding to the length of said pieces.
 19. In apparatus as setforth in claim 18, said control means further comprising means adaptedto initiate stepping of said motor after the trailing end of the longerpiece passes said first sensor unit.
 20. In apparatus as set forth inclaim 19, said control means further comprising a second counter adaptedto accumulate a count equal to the number of steps made by said motorand a comparator adapted to stop said stepping motor from furtheradjusting said variable speed drive until said trailing ends have bothpassed said second sensor unit when the count accumulated by said firstcounter equals the count accumulated by the second counter.
 21. Inapparatus as set forth in claim 20, said control means furthercomprising a third counter adapted to accumulate a count equal toone-half the count accumulated by the first counter; a fourth counteradapted to accumulate a count analogous to the time period between thepassage of the two trailing ends by said second sensor unit; and asecond comparator adapted to cause said stepping motor to drive a numberof steps equal to the difference in the count accumulated by said thirdcounter and the count accumulated by said fourth counter, said secondcomparator causing said stepping motor to vary the speed of said onefeed device to bring the trailing ends of the pieces substantially intoregistration in a length of travel of the trailing ends of said piecesgenerally corresponding to half the length of said pieces.
 22. Inapparatus as set forth in claim 1, means for causing both feed devicesto feed at substantially the same rate before said sensing means hassensed an out-of-registration condition of the trailing end of one ofsaid pieces relative to the trailing end of the other.
 23. In apparatusas set forth in claim 2, said control means further comprising means forcausing the one feed device to feed at substantially the same rate asthe other feed device before the sensing means has sensed anout-of-registration condition of the trailing ends of the two pieces,said means for controlling the variable speed drive being responsive tothe means for causing both feed devices to feed at substantially thesame rate.
 24. In apparatus as set forth in claim 23, said means forcausing both feed devices to feed at substantially the same ratecomprising a sensor adapted to provide a signal when both feed devicesare feeding at substantially the same rate, the control means beingresponsive to said signal to cease further adjustment of the variablespeed drive until the trailing ends of the two pieces have passed thesensing means.
 25. In apparatus as set forth in claim 1, thespeed-varying means comprising means for varying the speed of one feeddevice, the other feed device operating at a substantially constantrate.
 26. In apparatus as set forth in claim 4, means mounting saidfirst sensor unit for movement between its operative position and aposition adjacent said second sensor unit for facilitating entry of thepieces into the two sensor units.
 27. Apparatus for joining two piecesof material such as textile fabric comprising: means for seaming the twopieces of material together; means for feeding the two pieces throughthe seaming means comprising a first feed means for one of said piecesand a second feed means for the other with one of the latter a variablespeed feed means; means for sensing any out-of-registration condition ofthe trailing end of one of said pieces relative to the trailing end ofthe other piece as they are fed through the seaming means by the feedmeans; and means controlled by said sensing means for varying the speedof the variable speed feed means to vary the speed of feed of the pieceof material being fed thereby through the seaming means to bring thetrailing ends of the pieces substantially into registration one with theother.